The invention relates to a control valve for a device for changing the control times of an internal combustion engine according to the preamble of Claims 1 or 2 and to a device for changing the control times of an internal combustion engine according to the preamble of Claim 18.
In internal combustion engines, camshafts are used for actuating the gas-exchange valves. Camshafts are mounted in the internal combustion engine in such a way that cams located on these camshafts contact cam followers, for example, cup tappets, finger levers, or rocker arms. If a camshaft is set in rotation, then the cams roll on the cam followers, which actuate, in turn, the gas-exchange valves. Through the position and the shape of the cams, both the opening period and also the opening amplitude, as well as the opening and closing times of the gas-exchange valves are set.
Modern motor concepts involve the variable design of the valve train. On one hand, the valve stroke and valve opening period should have a variable form up to complete shutdown of the individual cylinders. For this purpose, concepts, such as switchable cam followers or electrohydraulic or electrical valve actuators are provided. Furthermore, it has been shown to be advantageous during the operation of the internal combustion engine to be able to influence the opening and closing times of the gas-exchange valves. In this way, it is especially desirable to influence the opening or closing times of the intake or exhaust valves separately, in order to selectively set, for example, a defined valve overlap. By setting the opening or closing times of the gas-exchange valves as a function of the current characteristic map range of the motor, for example, as a function of the current rotational speed or the current load, the specific fuel consumption can be lowered, the exhaust-gas behavior can be positively influenced, the motor efficiency, the maximum torque, and the maximum output can be increased.
The described variability of the gas-exchange valve control times is achieved through a relative change in the phase position of the camshaft with respect to the crankshaft. In this way, the camshaft is usually in driven connection with the crankshaft via a chain, belt, or gear train or drive concepts with an identical function. Between the chain, belt, or gear train driven by the crankshaft and the camshaft there is a device for changing the control times of an internal combustion engine, also called camshaft adjuster below, which transfers the torque from the crankshaft to the camshaft. Here, this device is constructed such that during the operation of the internal combustion engine, the phase position between the crankshaft and the camshaft can be held reliably and, if desired, the camshaft can be rotated within a certain angle range with respect to the crankshaft.
In internal combustion engines with a camshaft for the intake and the exhaust valves, these can each be equipped with a camshaft adjuster. Therefore, the opening and closing times of the intake and exhaust gas-exchange valves can be shifted in time relative to each other and the valve overlap can be set selectively.
The position of modern camshaft adjusters is usually located on the drive-side end of the camshaft. The camshaft adjuster can also, however, be arranged on an intermediate shaft, a non-rotating component, or the crankshaft. It is comprised of a drive wheel, which is driven by the crankshaft and which maintains a fixed phase relationship with respect to the crankshaft, a driven part in driving connection with the camshaft, and an adjustment mechanism transferring the torque from the drive wheel to the driven part. The drive wheel can be constructed as a chain, belt, or gear wheel in the case of a camshaft adjuster not arranged on the crankshaft and is driven by the crankshaft by a chain, belt, or gear train. The adjustment mechanism can be operated electrically, hydraulically, or pneumatically.
Two preferred embodiments of hydraulically adjustable camshaft adjusters represent the so-called axial piston adjuster and rotary piston adjuster.
In the axial piston adjusters, the drive wheel connects to a piston and this is connected to the driven part each by helical gears. The piston separates a hollow space formed by the driven part and the drive wheel into two pressure chambers arranged axial with respect to each other. If one pressure chamber is charged with pressure medium, while the other pressure chamber is connected to a tank, then the piston is shifted in the axial direction. The axial shifting of the piston is translated by the helical gears into a relative rotation of the drive wheel with respect to the driven part and thus the camshaft with respect to the crankshaft.
A second embodiment of hydraulic camshaft adjusters are the so-called rotary piston adjusters. In these adjusters, the drive wheel is locked in rotation with a stator. The stator and a rotor or driven element are arranged concentric to each other, wherein the rotor is connected to a camshaft, a projection of the camshaft, or an intermediate shaft with a non-positive, positive, or material fit, for example, via a press fit, screw or weld connection. In the stator there are several hollow spaces, which are spaced apart in the peripheral direction and which extend outward in the radial direction starting from the rotor. The hollow spaces are bounded in a pressure-tight way in the axial direction by a side cover. In each of these hollow spaces, a vane connected to the rotor extends, which divides each hollow space into two pressure chambers. Through selective connection of the individual pressure chambers to a pressure medium pump or to a tank, the phase of the camshaft can be set or held relative to the crankshaft.
For controlling the camshaft adjuster, sensors detect the characteristic data of the engine, such as, for example, the load state and the rotational speed. This data is fed to an electronic control unit, which controls the supply and discharge flows of pressure medium to the different pressure chambers after comparing the data with a characteristic data map of the internal combustion engine.
To adjust the phase position of the camshaft with respect to the crankshaft, in hydraulic camshaft adjusters one of the two counteracting pressure chambers of a hollow space is connected to a pressure medium pump and the other is connected to the tank. The supply of pressure medium with respect to a chamber in connection with the discharge of pressure medium from the other chamber shifts the piston separating the pressure chambers in the axial direction, whereby the camshaft is rotated relative to the crankshaft by means of helical gears in axial piston adjusters. In rotary piston adjusters, the vane is shifted by pressurizing one chamber and decreasing pressure from the other chamber and thus the camshaft is rotated relative to the crankshaft. To maintain the phase position, both pressure chambers are connected either to the pressure medium pump or separated both from the pressure medium pump and also from the tank.
The pressure medium flows to or from the pressure chambers are controlled via control valves, usually by means of a 4/3 directional proportional valve. This has a valve housing, which is provided with a connection for the pressure chambers (working port) and at least two supply ports. At least one of the supply ports is used as a feed port, through which pressure medium is fed from a pressure medium pump to the control valve. In addition, another supply port is used as a discharge port, through which the pressure medium leaving the pressure chambers is guided. Here, it can be provided, for example, that the discharge port communicates with a tank.
Within the essentially hollow, cylindrical valve housing, an axially displaceable control piston is arranged. The control piston can be brought axially into any position between two defined end position by means of an electromagnetic, pneumatic, or hydraulic actuating element, against the spring force of a spring element. The control piston is further provided with control edges, whereby the working ports can be connected to the supply ports and thus the individual pressure chambers or groups of pressure chambers can be connected selectively to the pressure medium pump or the tank. Likewise, a position of the control piston can be set, in which the pressure medium chambers are separated both from the pressure medium pump and also from the pressure medium tank.
Such a control valve is known from U.S. Pat. No. 6,363,896 B1. This is made from an essentially hollow, cylindrical valve housing and a control piston arranged displaceable in this housing in the axial direction. Two working ports, a feed port, and a discharge port are formed on the valve housing. The two working ports and the feed port are constructed as openings spaced axial with respect to each other in the cylindrical casing surface of the valve housing. Here, the feed port lies in the axial direction between the two working ports. In addition, an axial discharge port is provided, by which pressure medium can be discharged from the control valve.
Within the valve housing there is a control piston, which can be shifted by an electromagnetic actuating unit in the axial direction relative to the valve housing. An annular groove is provided, via which either the first or the second working port can be selectively connected to the feed port as a function of the position of the control piston with respect to the valve housing.
The discharge port can be connected either directly to one working port or to the other working port by a pressure medium duct formed within the control piston as a function of the relative position of the control piston within the valve housing.
Furthermore, a supply line is provided, through which the feed port communicates with a pressure medium pump, which feeds pressure medium continuously to the control valve.
The position of the feed port between the working ports requires a complicated pressure medium guide within the driven element. For one, both radial pressure medium lines starting from one of the working ports and also axial supply lines starting from the radial supply port are located within an axial part of the driven element. This accumulation of lines in an axial part decreases their maximum through-flow cross sections.
Another disadvantage comes from the fact that a connection between the axial supply lines and the radial pressure medium lines must be prevented. For this purpose, in the state of the art, the supply lines are constructed by several thin boreholes communicating with each other, by which pressure medium is fed from a camshaft bearing to the feed port. The construction of these boreholes is very expensive and susceptible to errors. In addition, the processing reliability suffers, because thin drills tend to break off when the boreholes are formed.